Means and method of photographically recording sound



Dec.'13,1938. J. E-NGL EI'AL 0 2,140,003

MEANS AND METHOD OF PHOTOGRAPHICALLY RECORDING SOUND Filed April 4, 1921d :4 0 OZ INVENTORS: Fl L/OSEPH P7055015 m 0 IZIINS 1 007- 7 HF. OJEF EN61.

Patented Dec. 13, 1938 UNITED STATES arrests PATENT OFFICE MEANS ANDMETHOD OF PHOTOGRAPHI- CALLY RECORDING SOUND Application April 4, 1921,Serial No. 458,631 In Germany June 2, 1919 3 Claims.

It is generally known that sound vibrations can be recordedphotographically by influencing in the rhythm of the acousticfrequencies light rays which act upon a suitable light-sensitive mediumor phonogram carrier. For the purposes of acoustic kinematography therehas chiefly been used hitherto an electric are as a source of light,which is adapted to be influenced by sound vibrations under certainconditions.

The use of arc discharges for the photographic recording of soundvibrations has however the disadvantages that owing to the inertia ofthe arc comparatively large variations of resistance are required tosecure an influence which is perceptible and sufficient for photographicpurposes. The further difliculty, of ensuring the required constancy inthe average intensity of the light or its intensity when not modulatedby the sound to be recorded, and in particular of preventing the arcfrom becoming totally extinguished periodically, has hitherto not led toa practically satisfactory method of enabling the optical andparticularly the photographical recording of sound waves for thepurposes of acoustic kinematography. For the last mentioned field ofapplication irregularities in the source of light are particularlydisadvantageous, as it is here important to ensure that the source oflight shall be influenced only in accordance with the sound waves whichare to be recorded.

This invention provides means for producing photophonograms,particularly for acoustic kinematography, by means of a source of lightwhich ensures solely the influencing thereof by sound waves withoutitself bringing any source of error into the procedure. With this objectin view the glow light discharge, known of itself for other purposes,and which is dependent on the strength of the current in the dischargetube, is used as the source of light. As glow light tubes can beoperated by small currents, relatively and absolutely small alterationsof resistance suffice, in contradistinction to the hitherto knownsources of light, in order to obtain great fluctuations of intensitywith a sharper and more rapid control of the intensity of the light.Consequently the most accurate and most delicate photographic recordingof the sound vibrations is possible.

The photographic influence upon the moving strip of film, sensitive tolight, or other lightsensitive surface, may be effected in such a mannerthat, by means of an acoustically controlled source of light (glowlight), linear transverse blackenings are produced which standperpendicular to the direction in which the strip of film is fedforward.

According to this invention the acoustic Variation of these blackeningsis effected either with a constant width of the blackenings, i e., theirdimension transverse to the direction of movement, by varying theintensity of the exposure, or with a constant exposure by lateralvariations of the width of the blackenings. As, with the variation ofintensity the exposure capacity of the bromide of silver coating imposesnarrow and not easily controllable limits upon the variation of thesource of light, the variation of the width of blackening is, to thisextent, preferable, as it permits of an easier adjustment of the maximumelongation and, owing to the possibility of widening the strip of film,of a greater clearness in the recording of the sound marks. Thedifliculties referred to in connection with the variation of intensitymethod may, however, be overcome by means not here described.

The invention comprises the means for and method of photographicallyrecording sound, by means of a source of light of the character referredto, maintained quite closely at constant intensity except as it isacoustically-varied, this light source specifically being a glow lightdischarge, as will be more fully set forth in the followingspecification, and be particularly pointed out in the appended claims.The invention also consists in the various combinations of elements,steps of process, etc., all as will be more fully set forth hereinafter,and pointed out in the appended claims.

In order that the invention may be clearly understood, we will proceedto describe the same with reference to the different forms ofconstruction shown by way of example in the accompanying drawing,wherein:-

Fig. 1 illustrates diagrammatically a method for the lateral variationof the blackening.

Fig. 2 is a view similar to Fig. 1 showing other means for carrying outthe method, with variations of intensity.

Figs. 3 and 4 show parts of a film strip with different forms oflaterally varying blackening.

Figs. 5 and 6 are diagrams of connections used in connection with theimproved method.

Fig. 7 is a diagram of connections for the glow light tube shown in Fig.1.

The method can be carried out in such a manner that by varying theresistance of a microphone in use electrical alternating currents areproduced the shape of whose curve corresponds with the sound phenomenon.This energy can for example be supplied to the glow light tubes by meansof amplifiers and transformers. Owing to the small amount of electricalpower necessary to keep up the glow light discharge only smallalternating currents, excited by the sound operation, are required forthe control of the glow light discharge, and are sufficient to allow thevariation of light to follow the most rapid of acoustic frequencies. Thegas used in the light tube is preferably so selected that the wavelength of the light emitted has the best possible photographical effect.

The method for the lateral variation of. the lines of theblackening'can, as shown diagram matically in Fig. 1, be carried out ina manner that the negative glow light is used which is produced at thecathode of a glow light tube R, when it has the form of a long straightwire (1 or of a narrow strip of sheet metal. The length of this cathodelight is fairly in proportion to the discharge current- This phenomenonwhich accompanies, with sufficient lack of inertia, even high frequencydischarge processes, is already utilized with glow light oscillographsfor the photographic examination of alternating currents. In connectionwith the constructional formof glow light tube shown in Fig. 1acoustically influenced high frequency alternating current is used asglow light current and it produces at both electrodes, which alternatelybecome the cathode, a luminous layer sch. of varying length. The pencilof rays acting upon the film may be brought to the dimensions requiredby means of a system of lenses Z and of a slit in plate S. By means of areflector, not shown, the intensity of the light acting upon the filmmay be increased. Preferably the amount of light'impinging is selectedof such magnitude that the film is overexposed at 'the pointsilluminated. The developed film has then the appearance shown in Fig. 3.If, instead of high frequency alternating current, acousticallyinfluenced direct current be used as glow light current, the film willhave the appearance shown in Fig. 4.

Conventional circuit connections for the glow light tube R of Fig. 1, asdescribed above, are indicateddiagrammatically in Fig. '7, in which themicrophone M is shown conventionally as connected in a conventionalmanner to the input circuit of an amplifier tube Vr. The output circuitof tube V7" is shown as connected to the terminals of the electrodes ofthe glow light tube R, as shown in Fig. 5. The high frequencyalternating current, used as glow light current in this form ofconstruction, as. stated, maybe introduced into the circuit in any usualmanner. The connection from a suitable source of high frequency currentis indicated conventionally in Fig. 7 at the coil marked H. F. If directcurrent is used as glow light current, as in Fig. 2, the high frequencyconnection is, of course, omitted, and the terminal voltage for the glowlight tube supplied, for example, by battery I) in Fig. 5, or battery bin Fig. 6, hereinafter described.

The method for the alteration of the intensity of the exposure can becarried out, for instance, as shown in Fig. 2. The discharge area of theglow light tube R as there shown may have the form of a capillary 7c,the thin linear light area of which permits of a better concentration oflight. The light is thrown, if necessary by means of reflector, upon thefilm. F by a. suitable system of lenses Z and by the slit of the plateS. Upon this film, within its areas of exposure, stripes or lines areproduced, the darkening or blackening of each of which is uniform inintensity over the whole width of the film, that is throughout thelength of each line, the various lines differing, however, from eachother in intensity of blacken- By inserting in the path of the lightrays a light diminishing, wedge-shaped body e part of the light will beabsorbed by the same according ,to the degree of its transparency. Thuswith increasing thickness of the wedge, the film will be gradually lessblackened throughout its width. For the complete blackening a greaterquantity of light is however necessary, which is determined in themaximum by the maximum thickness of the wedge, whilst the minimumquantity of light determined by the thinnest part of the wedge and stillcapable of causing exposure, is not materially increased by the wedge.The wedge enables consequently larger variations of light to be obtainedbetween the exposure limits, which are also eifectiveowing to thelateral variation in darkening or blackening. The photographic pictureresulting will be similar to that shown by Fig. 4 with the modificationthat, in the lateral direction there is only present a gradualtransition from the lowest to the strongest exposure.

In further pursuance of the invention the novel method is preferablycarried out in such wise that, for controlling the strength of the glowcurrent, the electro-acoustic currents are amplified to correspond tothe desired current and voltage conditions. For this purpose specialamplifying arrangements are required, into the circuit of which the glowlight tube R. is inserted. Of course, as is well known, a glow lightdischarge can, owing to its characteristic feature, only be maintainedin series witha large resistance. For this purpose use can be made (Fig.5) of the internal resistance between the cathode and anode of thevacuum tube amplifier Vr, which tube may be the last of a series. Acertain amount of inaccuracy may, however, appear with such aconnection, because the internal resistance of the amplifier may varyconsiderably with changes in the acoustically-modulated current in theinput circuit thereof. If the discharge of the glow discharge tube berepresented by a current-voltage curve the voltage will be seen to dropslightly as the current is increased. The discharge of the glowdischarge tube, connected in series with the amplifier, may at anymoment be represented by a point on this characteristic curve, and therapid changes in internal resistance of the amplifier may cause thispoint to move excessively to and fro over the characteristic. Thismovement. of this point means that the discharge will not be as'stableas might be desired, and the movement of this theoretic point should,therefore, for best results be maintained Within a somewhat narrowlimit. Such connections are indicated in Fig. 5, in which the req uisiteterminal voltage for the discharge circuit is supplied by the sourceindicated as battery I) in the amplifier-glow tube circuit shown in Fig.5. In this case the difiiculty mentioned above may be observed, and theacoustically-modulated discharge phenomenon in glow tube R may not be asstable as is desired. This difiiculty may be cor-' rected by insertingthe glow light tube R in a second circuit, Fig. 6, inductively coupledto the circuit in which is connected the last vacuum tube, V7, of theamplifying series. This coupling is shown in Fig. 6 as the transformert1, having primary a and secondary It. When this is done the movement ofthe point mentioned, on the characteristic, becomes less marked, becauseof the fact that the resistance of the secondary winding of thetransformer coupling is constant and the variations in resistance of theamplifier will not have as great an effect upon the glow discharge tube.

A battery M in the circuit h supplies the necessary medium or averageworking voltage, which, through the superimposed induction E. M. F., ismagnified or reduced in the acoustic rhythm. By proper selection of thecoupling the acoustic modulation of the light of tube R can be alteredin the manner desired.

It will be noted that the glow discharge tube or glow light tube hereindescribed is an enclosed luminous gas discharge device which ismaintained very closely at constant luminosity, or the luminosity ofwhich is efiectively constantly luminous, when the current feeding thesame is not acoustically-modulated. This current, as stated, may be highfrequency alternating current or direct current. When sound waves arereceived by the microphone in the system the current reaching the gasdischarge device is acoustically-modulated, and the luminosity of thedevice, or lamp, is accordingly varied by and in accordance with thesound waves, or, phrasing it differently, by and in accordance withtelephonic currents. The light thus varied is directed to a sensitizedelement, the moving film, to make a photographic record thereon asdescribed.

When alternating high-frequency current is used the frequency should beabove the audible limits, as is obvious to those skilled in the art,

in order that the noises produced by the alternating current should notbe reproduced, when reproduction of the recorded sound is efiected.

We claim:

1. In an apparatus for the production of photophonograms, a capillaryglow light tube, a microphone circuit by which said tube is controlled,a slotted plate, a lens between the plate and tube, and a wedge-shapedlight absorbing body between the plate and film.

2. Means for photographically recording sound waves comprising anenclosed luminous gas discharge device of a type producing a negativeglow discharge, means for constantly maintaining said device with thenegative glow discharge thereof effectively luminous, and means forvarying the luminosity of said negative glow discharge of said device byand in accordance with sound waves, and means for directing the lightfrom the negative glow discharge of said device to a sensitized element.

3. The method of photographically recording sound which comprisesvarying the luminosity of the negative glow discharge in an effectivelyconstantly luminous enclosed gas discharge device of a type producing anegative glow discharge, such varying of the luminosity of the negativeglow discharge being effected by and in accordance with sound waves, anddirecting light from said varying negative glow discharge onto a movinglight sensitive surface.

JOSEF ENGL. JOSEPH MASSOLLE. HANS VOGT.

